Module Atmosphere - Revision history

Davidbrito: /* Random components */

2015-06-26T14:05:38Z

‎Random components

Davidbrito: /* Cloud cover */

2015-06-26T14:05:10Z

‎Cloud cover

Jauch at 16:09, 8 November 2010

2010-11-08T16:09:11Z

Davidbrito: /* Links */

2009-03-12T18:28:15Z

‎Links

Davidbrito: /* User Manual */

2009-03-12T18:27:39Z

‎User Manual

Guillaume: 1 revision

2008-12-03T10:27:17Z

1 revision

193.136.128.7 at 13:11, 14 August 2008

2008-08-14T13:11:42Z

New page

== Overview ==
The atmosphere module is responsible for meteorological data needed to compute processes occurring at the water-air interface, such as computing wind shear stress, radiation balances, latent and sensible heat fluxes.

A user manual is available in the link at the bottom of the page. This user manual intends to help the user to couple atmosphere to water, activating in MOHID wind forcing, heat fluxes and mass fluxes between this interface.

== Concepts ==

== Main processes ==

=== Air temperature ===
Air temperature is used for latent heat, sensible heat and downward longwave radiation computation (in the atmoshphere-water interface).

=== Solar radiation ===
Heat flux with solar origin hitting the water surface.
In absence of field data it can be computed based on two approaches that depend both on Top Of Atmosphere Radiation, sun height and cloud cover:

i) MOHID (default method)

ii) CE-QUAL based method.

Solar radiation is used to compute radiation that enters the water surface (after reflection). One method for cloud cover computation also uses radiation as input.

=== Wind ===
Wind is described by its velocity decomposed on x and y components. If not available it can be computed from wind modulus and wind direction.

Wind is used to compute latent heat, sensible heat and wind stress (in the water-atmoshphere interface).

===Specific humidity===
Specific humidity is the ratio of water mass present in the atmosphere against the air mass. Moisture mixture is the ratio of water mass against that of dry air. Relative humidity can be computed from specific humidity, pressure and air temperature when not given.

=== Relative humidity ===
Relative humidity is a term used to describe the amount of water vapor that exists in a gaseous mixture of air and water.
The relative humidity of an air-water mixture is defined as the ratio of the partial pressure of water vapor in the mixture to the saturated vapor pressure of water at a given temperature.

Relative humidity is used for latent heat computation (in the water-atmoshphere interface).

=== Precipitation ===
Mass Flux from rain.

=== Sun hours ===

=== Cloud cover ===
Fraction of sky covered with clouds. Represents the radiation absorption in the atmosphere.
It can be computed from three approaches:

i) comparison between measured sun hours (if available) with potential sun hours;

ii) comparison between solar radiation (measured or computed) and top of atmosphere radiation;

iii) random solution (default method).

Cloud cover is used for downward long wave radiation computation (in the atmoshphere-water interface). One method in solar radiation computation (if no data available) uses cloud cover as input.

'''Remarks''':

* Random solution is default method but it shoud not.

* Cloud cover should never be computed from computed radiation. This latter situation returns always zero cloud cover and zero radiation in the results (*).

* Cloud cover computation from measured radiation has the advantage that is not a random calculation but has the disadvantage that returns the same trend as radiation data: meaning that every day at night sky is completely covered with clouds and reaches minimum cloud cover at solar mid day. It may not be realistic for heat budgets at night.

(*)This appens because the model is initialized with zero radiation; then, if cloud cover is computed from radiation it returns zero cloud cover (**) in next time step which in turn results in zero transmissivity and zero radiation, going on cycle.

(**) in MOHID code for cloud cover computation from radiation, cloud cover units are different than standard, being value 1 the situation with no clouds and zero the opposite.

=== Irrigation ===
Mass flux from water added by anthropogenic sources.

== Other features ==

=== Random components ===
Cloud cover computation has as it default method a random method. This method was adapted from CE-Qual formulation.
See cloud cover for further information.

== User Manual ==
[[Coupling_Water-Atmosphere_User_Manual]]

== Links ==

*[[Module_InterfaceWaterAir]]
*[[ConvertToHDF5]]

[[Category:Modules]]
[[Category:MOHID Base 2]]

← Older revision		Revision as of 14:05, 26 June 2015
Line 88:		Line 88:

	=== Random components ===		=== Random components ===
−	~~Cloud cover computation has as it default method a random method. This method was adapted from CE-Qual formulation.~~
−	~~See cloud cover for further information.~~

	== User Manual ==		== User Manual ==

@@ Line 46: / Line 46: @@
 i) comparison between measured sun hours (if available) with potential sun hours;
-ii) comparison between solar radiation (measured or computed) and top of atmosphere radiation;
+ii) random solution (this option was removed from June 2015, it is shown here for user help).
 Cloud cover is used for downward long wave radiation computation (in the atmoshphere-water interface). One method in solar radiation computation (if no data available) uses cloud cover as input.
@@ Line 54: / Line 55: @@
 '''Remarks''':
-* Random solution is default method but it shoud not.
+* Cloud cover can not be computed from computed radiation because cloud cover will use computed radiation and radiation uses computed cloud cover ("pescadinha de rabo na boca" situation). This returns always zero cloud cover and zero radiation in the results (*).
-* Cloud cover computation from measured radiation has the advantage that is not a random calculation but has the disadvantage that returns the same trend as radiation data: meaning that every day at night sky is completely covered with clouds and reaches minimum cloud cover at solar mid day. It may not be realistic for heat budgets at night.
+* Cloud cover computation from measured radiation has the advantage that is not a random calculation so it was used as default method after June 2015.
-(**) in MOHID code for cloud cover computation from radiation, cloud cover units are different than standard, being value 1 the situation with no clouds and zero the opposite.
+(*)This happens because the model is initialized with zero radiation; then, if cloud cover is computed from radiation it returns zero cloud cover in next time step which in turn results in zero transmissivity and zero radiation, going on cycle.
 === Irrigation ===

@@ Line 67: / Line 67: @@
 === Irrigation ===
 Mass flux from water added by anthropogenic sources.
 == Other features ==
@@ Line 79: / Line 98: @@
 == Links ==
-*[[Module_InterfaceWaterAir]]
+*'''[[Module_InterfaceWaterAir]]'''
-*[[ConvertToHDF5]]
+*'''[[ConvertToHDF5]]'''
-*[[FillMatrix]]
+*'''[[FillMatrix]]'''
 [[Category:Modules]]
 [[Category:MOHID Base 2]]

@@ Line 75: / Line 75: @@
 == User Manual ==
-[[Coupling_Water-Atmosphere_User_Manual]]
+[[Coupling_Water-Atmosphere_User_Manual| Coupling Water-Atmosphere User Manual]]
 == Links ==

← Older revision	Revision as of 10:27, 3 December 2008
(No difference)